This is a neat idea! Pretty simple design using materials you could find at a large hardware store. I think I’d spray paint it to match the color of the walls. What lucky kitties!
Check out this post on incredible cat ladders in Europe!
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Some of these materials could be found at a hardware store but very unlikely the wire mesh. It is pvc-coated and virtually rust-proof. Paint would not adhere to it very well, and lighter colours actually draw more attention as they reflect light. This project is near Victoria, BC, Canada and was built by Beautiful World Living Environments. See also https://www.pinterest.com/cats4all/cat-enclosures-for-other-animals-too-from-catscape/